As power source has developed towards high power density nowadays, besides circuit structure itself, suitable component choices and circuit parameters optimization, non-conventional electrical design including electrical mechanism, thermal design and adequate printed circuit board (PCB) arrangement are becoming more significant in the actual design of power source to achieve higher efficiency. In power source design, the design of magnetic core element is particularly important due to the high frequency caused by high power density. Moreover, the design for power transformer is also a crucial point, especially in high power and high frequency applications. For example, the whole structure of a conventional DC/DC converter is shown in FIG. 1. The secondary side of a transformer 1 includes secondary windings, output rectifiers 3 and an output filter 4, while the primary side of the transformer 1 includes primary windings and primary switches 2. The primary switches 2 connect to an input terminal 5, and the output filter 4 is connected to a load 6. Increasing the frequency of the circuits' switches can effectively reduce the volume of the magnetic core element; however, this higher frequency generates numerous issues in the winding design of a transformer. Skin depth effect and proximity effect of conducting wires in high frequency operation will cause additional power loss on transformer windings itself and there between, especially apparent in high current output. Further, the output side structure of a conventional transformer is shown in FIG. 2, and the windings of the transformer 1 are connected to the primary switches 2, the output rectifiers 3 and filter 4. The rectifiers 3 and filters 4 of the output side are configured on a PCB, and Zp indicates parasitic impedance on the wires. Such arrangement results in secondary side wires of the transformer 1 extend a larger distance to the output rectifier and longer alternative passage. As a result, tremendous loss will occur on the equivalent parasitic resistance of the wires in high frequency and large current applications, such that the switch elements cause more switching power loss to affect reliability and efficiency of the circuits. Similarly, terminal power loss of the output windings of the conventional large power transformer 1 will be increased substantially due to terminal effect.
Accordingly, it has become an important factor to design a better transformer windings structure and output side structure for improving circuit reliability and efficiency. Thus, for the drawbacks of the prior art and numerous unfavorable features from conventional transformers discussed above, the present invention provides a novel transformer structure which can effectively reduce the length of AC wires and transformer's power loss, and thereby enhance the efficiency of the whole circuits.